IEnumerator and yield

Learn to use IEnumerator and yield return null.

IEnumerator and yield return null

For Unity to recognize a method as a coroutine, it must return the IEnumerator interface from System.Collections and contain at least one yield statement in its body.

using System.Collections;

IEnumerator StepRoutine() {
    // Wait for one frame
    yield return null;
}

The yield return null; instruction tells Unity that the current frame is yielded and execution must resume on the very next frame.

Early exit with yield break

When a specific condition requires terminating a running coroutine early, yield break; is invoked. Operating much like return; in regular methods, it shuts down the coroutine entirely.

IEnumerator HealthMonitor(int hp) {
    if (hp <= 0) {
        yield break; // Halts coroutine when health is depleted
    }
    yield return null;
}

This prevents superfluous iteration cycles and maintains performance optimization.

Exercise Print return and yield state

Assign "IEnumerator" to returnType and "null" to yieldState. Print Return: IEnumerator | Yield: null to the console.

Show example solution

using System;

class Program
{
    static void Main()
    {
        string returnType = "IEnumerator";
        string yieldState = "null";
        Console.WriteLine("Return: " + returnType + " | Yield: " + yieldState);
    }
}

Test yourself

Which statement is written inside a coroutine to wait precisely until the next frame?
- return 0;
- yield break;
- Thread.Sleep(1000);
- yield return null;
Show answer

yield return null; — yield return null is the standard statement that pauses the coroutine until the following frame.
Yield until next frame
```
yield return ____;
```
Show answer
```
yield return null;
```
IEnumerator and yield terms

IEnumerator

Coroutine mandatory return type
yield return null

Wait until next frame
yield break

End coroutine execution now
System.Collections

Namespace holding IEnumerator

Next lesson: WaitForSeconds

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